1. Technical Field
The present invention relates to a method and a device for measuring a largeness of a working force during a press working of a mechanical press.
2. Description of the Earlier Technology
Conventionally, a strain gauge has been adhered to a pressure receiving structural portion such as a frame and a connecting rod of a mechanical press. When the pressure receiving structural portion undergoes a strain with a load imposed thereon, the strain has been detected to thereby measure a working force during a press working.
The conventional technique has a problem that it needs much labor so as to measure the working force and besides encounters a large measurement error.
More specifically, when adhering the strain gauge to the frame, the measured values greatly vary in correspondence with the portions where the strain gauge is adhered. Further, when adhering the strain gauge to the connecting rod, there may be caused a case where it is difficult to adequately adhere the strain gauge depending on the sectional shape of the connecting rod. Additionally, in accordance with the kind of the press working such as shearing and bending, the strain occurs at varying parts of the frame and the connecting rod and in changing largeness.
In consequence, the conventional technique must search a proper portion for adhering the strain gauge and calibrate the measured values by conducting many test workings in advance and detailedly comparing the values measured during the test workings with the actual working forces. Therefore, it takes much labor to measure the working force and besides a large measurement error occurs due to the above-mentioned various variations and changes.
Additionally, the conventional technique experiences a far larger measurement error of the working force because the strain of the pressure receiving structural portion varies depending on the change of the atmospheric temperature of the place where the mechanical press is installed and on the temperature increase of a driving force transmission system while the press working is performed.
Japanese Patent Publication No. 50-38228 discloses an invention which converts a load of a mechanical press to an oil pressure and stops the operation of the mechanical press when overload is produced. However, this invention is not adapted so as to be able to measure a working force during a press working.
The present invention has an object making it possible to precisely and easily measure the working force during the press working.
In order to accomplish the object, an invention of claim 1 has constructed a method for measuring a working force of a mechanical press in the following manner, for example, as shown in FIGS. 1 to 3.
A mechanical press 1 has a slide 3 within which an overload absorbing hydraulic chamber 12 is provided. The mechanical press 1 transmits its driving force to the slide 3 through pressurized oil charged into the hydraulic chamber 12. In correspondence with an initial pressure of the pressurized oil to be charged, a computer 33 stores a relationship between a pressure (P) of the pressurized oil which has been pressurized with a working force (F) during a press working and a largeness of the working force (F) as at least one pressurizing characteristic (A1, A2, A3, A4, A5, A6). When the computer 33 calculates each working force during a press working, first, a pressure of the pressurized oil is sensed before every press working and the sensed pressure is stored as a preload pressure (Pa1). Next, a maximum pressure of the pressurized oil which has been pressurized during the press working is sensed and the sensed pressure is stored as a peak pressure (Pb1). Thereafter, the computer 33 calculates a working force (F1) based on a pressurizing characteristic (A1) corresponding to the preload pressure (Pa1) and on the peak pressure (Pb1).
The method of the invention produces the following function and effect.
This invention makes it possible to calculate a working force during a press working by sensing a pressure of the pressurized oil within the hydraulic chamber. Accordingly, differently from the above-mentioned conventional technique of strain-gauge type, it can calculate the working force without taking a trouble to conduct many test workings. Besides, it can do the calculation irrespective of the change of the atmospheric temperature of the place where the mechanical press is installed and the temperature change of the driving force transmission system which occurs while the press working is performed. In addition, each time the mechanical press performs a press working, a preload pressure before the press working is taken in to calculate a working force during the press working. Therefore, no error is caused by the change of the preload pressure to result in the possibility of precisely and easily calculating an actual working force.
An embodiment for measuring a working force of a mechanical press is shown in FIGS. 1 to 3.
The device comprises an overload absorbing hydraulic chamber 12 provided within a slide 3 of the mechanical press 1, pressurized oil charged into the hydraulic chamber 12 and transmitting a press driving force to the slide 3, a pressure sensing means 27 for sensing a pressure of the pressurized oil and a computer 33 which operates based on the sensed signal of the pressure sensing means 27. In correspondence with an initial pressure of the pressurized oil to be charged, the computer 33 stores a relationship between a pressure (P) of the pressurized oil which has been pressurized with a working force (F) during a press working and a largeness of the working force (F) as at least one pressurizing characteristic (A1, A2, A3, A4, A5, A6). The computer 33 calculates a working force (F1) based on a pressurizing characteristic (A1) corresponding to a preload pressure (Pa1) sensed before every press working and on a peak pressure (Pb1) of the pressurized oil which has been pressurized during the press working.
More specifically, this invention can calculate a working force during a press working through sensing a pressure of the pressurized oil within the hydraulic chamber by the pressure sensing means. Accordingly, differently from the above-mentioned conventional technique of strain-gauge type, it can calculate the working force without taking a trouble to conduct many test workings. Besides, it can do the calculation irrespective of the change of the atmospheric temperature of the place where the mechanical press is installed and the temperature change of the driving force transmission system which occurs while the press working is performed. In addition, each time the mechanical press performs a press working, a preload pressure before the working is taken in to calculate a working force during the press working. Therefore, no error is caused by the change of the preload pressure to result in the possibility of precisely and easily calculating an actual working force.
Another embodiment of the present invention is preferably constructed in the following manner.
The computer 33 stores a plurality of pressurizing characteristics (A1), (A2), (A3), (A4), (A5) and (A6) for predetermined initial pressures of the pressurized oil to be charged, respectively. It selects at least one pressurizing characteristic (A1) corresponding to the preload pressure (Pa1) from among the plurality of pressurizing characteristics (A1), (A2), (A3), (A4), (A5) and (A6), and calculates a working force (F1) based on the selected at least one pressurizing characteristic (A1) and the peak pressure (Pb1).
This embodiment provides the computer with a plurality of pressurizing characteristics. Therefore, even if the initial pressure for charging the pressurized oil into the hydraulic chamber is changed or even if the initial pressure varies over a wide range, it can immediately adapt itself to the change and the variation. This can adapt the present invention promptly to a mechanical press of different capacity and to a press working of different kind.
Another embodiment of the present invention is preferably constructed in the following manner.
The computer 33 is connected to an actuator 24 for adjusting a die height. The calculated working force (F1) is compared with either a set range (X) or at least one set value. Based on the comparison, the actuator 24 is driven to thereby retain the working force (F) during the press working within a desired range.
Even if the mechanical press deforms due to thermal strain or a work to be supplied changes in thickness and hardness, the die height adjusting actuator adjusts the die height based on the precisely calculated working force, thereby being able to keep the working force within the desired range. This makes the working force during the press working almost constant and improves the working accuracy.
Another embodiment of the present invention is preferably constructed in the following manner.
In the case where the calculated working force (F1) is close to an upper limit value of the set range (X), the actuator 24 is driven in a direction for increasing the die height, and on the other hand in the case where the calculated working force (F1) is close to a lower limit value of the set range (X), the actuator 24 is driven in a direction for decreasing the die height, so as to retain the working force (F) during the press working within the set range (X).
This embodiment predicts a tendency of variation of the working force in advance, thereby being able to retain the working force within the set range. This results in further improving the working accuracy.
Another embodiment of the present invention is preferably constructed in the following manner.
Two set values of an upper limit value and a lower limit value are provided as the set value. In the case where the calculated working force (F1) is not less than the upper limit value, the actuator 24 is driven in a direction for increasing the die height, and on the other hand in the case where the calculated working force (F1) is not more than the lower limit value, the actuator 24 is driven in a direction for decreasing the die height, so as to retain the working force (F) during the press working within the desired range.
This embodiment maintains the working force within the desired range only by providing the two set values of the upper and lower limit values. Thus the working accuracy can be improved with a simple construction.
Another embodiment of the present invention is preferably constructed in the following manner.
The sensed preload pressure (Pa1) is compared with an initial pressure of the at least one pressurizing characteristic (A1, A2, A3, A4, A5, A6) and the working force (F1) is calculated based on a pressurizing characteristic obtained by the comparison and on the peak pressure (Pb1).
This embodiment includes a new pressurizing characteristic or selects a specific pressurizing characteristic through the comparison, thereby being able to calculate a working force based on a pressurizing characteristic most corresponding to the sensed preload pressure. This makes it possible to calculate an actual working force during a press working more precisely.
Another embodiment of the present invention is preferably constructed in the following manner.
The computer 33 is connected to an actuator 24 for adjusting a die height. The calculated working force (F1) is compared with either a set range (X) or at least one set value. Based on the comparison, the actuator 24 is driven to thereby retain the working force (F) during the press working within a desired range.
Even if the mechanical press deforms due to thermal strain or a work to be supplied changes in thickness and hardness, the die height adjusting actuator adjusts the die height based on the precisely calculated working force, thereby being able to keep the working force within the desired range. This makes the working force during the press working almost constant and improves the working accuracy.
Another embodiment of the present invention is preferably constructed in the following manner.
The sensed preload pressure (Pa1) is compared with an initial pressure of the at least one pressurizing characteristic (A1, A2, A3, A4, A5, A6). And the working force (F1) is calculated based on a pressurizing characteristic obtained by the comparison and on the peak pressure (Pb1).
It is possible to calculate a working force based on a pressurizing characteristic most corresponding to the sensed preload pressure by seeking a new pressurizing characteristic or selecting a specific pressurizing characteristic through the comparison. This makes it possible to calculate an actual working force during a press working more precisely.